Electronic devices, such as filters, amplifiers, Current Injectors (CINs), motor drivers and other electronic equipment, need to be protected against strong currents. Such strong currents can occur, for instance, due to strikes of lightning and thunder.
Such electronic devices are, in order to secure a proper operation of the system, often located in environmental hostile locations, for example on high buildings or constructions, such as base station antenna masts and the like. By strikes of lightning or thunder, high currents run along all conducting structures and also along cables being connected to the devices, thereby threatening the entire device, including the casing and the connectors of the device as well as the electronic components within the casing. Thus, in, for instance, a coaxial cable, strong currents run in both an inner conductor and an outer conductor of the cable, thereby causing harmful differential pulses between these conductors. Such differential pulses have traditionally been counteracted by the use of active lightning protection devices, in which Gas Discharge Tubes (GDTs) or the like are used for absorbing the currents.
Traditionally, casings for such electronic devices have been made of metal or metal alloys, such as aluminum alloys, which have also protected the devices, since the metal cases then could be designed to be able to cope with such strong currents. Traditionally, by leading the strong currents through the casing, either between the connectors or to some robust grounded construction, the devices have been protected.
However, in order to make production costs as low as possible, it is advantageous to make the casings and other parts of these devices in less costly and more easily processed materials. Such a low cost material is, for instance, plastics. Such preferred low cost materials are all essentially non-conducting. However, many of the devices must have a metal coating, i.e. a thin layer of metal, being arranged on the inside of the plastic walls and other parts, in order to operate properly.
In this document, “conducting” means electrically conducting whereas “non-conducting” means electrically non-conducting, as is clear for a skilled person.
For such casings, being made of an essentially non-conducting material and being coated by a metal coating, the coating of the casing has to be protected against strong currents running through an outer shield conductor of a cable being connected to the electronic device. This can be done by the use of a passive lightning protection, letting the strong current bypass the casing. Such a passive lightning protection device, not including active components such as GDTs or the like, is known from prior art document WO 2004/097979. Preferably, an electronic device should include both a passive and an active lightning protection, in order to be properly protected against strikes of lightning.
FIG. 1 shows a prior art microwave transmission unit 100 from document WO 2004/097979, where the microwave transmission unit 100 is provided with a passive lightning protection arrangement. Here, a cabinet 110 of the unit is made of plastic and is coated with a thin metal layer, and the connectors 120, 121 are made of metal. In order not to destroy the metal layer of the coating, the unit is also provided with metal fittings 130 leading strong currents from the metal connectors 120, 121, through the fittings 130 and to a metal lightning conductor, preferably being located in the cover 111 of the cabinet, thereby leading the current away from the inside of the cabinet 110. The fittings 130 are fastened to the metallic connectors 120, 121 by the use of screws 131 being attached to a metallic plate 122 of the connectors 120, 121, thereby leading away strong currents being present on the shielding conductor of the connectors.
In WO 2004/097979, some parts of the microwave transmission unit 100, such as the connectors 120, 121 and the lightning conductor, such as the cover 111, still have to be made of metal in order to protect the unit, which add to the production costs. Thus, in this prior art unit, there is a problem how to achieve a low cost unit having a secure and efficient lightning protection.
Aim and Most Important Features of the Invention
It is a main object of the present invention to provide a passive surge protection arrangement that solves the above stated problem.
The present invention aims to provide an efficient surge protection arrangement, being less costly and easier to produce than the lightning protection devices known in the prior art.
The main object is achieved by a surge protection arrangement according to the characterizing portion of claim 1, i.e. the connector body is made of a non-conducting material, and the internal coupling device includes                a conducting protection sleeve, in use being in electrical contact with the outer shield conductor of the transmission cable, and        at least one conducting diversion member, in use being in electrical contact with the protection sleeve, and extending radially outwardly from the protection sleeve, through the connector body, to at least one metallic structure being in permanent electric contact with ground and having a high capacity of conducting strong currents.        
The surge protection arrangement according to the present invention will offer a safe protection of an electronic device essentially entirely being made of a non-conducting material.
Thus, with the present invention, the casing as well as the connectors of the device can be made in a low cost non-conducting material, being easily manufactured, and still be safely protected against surges.
This is possible, according to the present invention, since the strong currents are diverted from the internal coupling device of the connector, through the non-conducting connector body, and to a metallic structure being in permanent electrical contact to ground and also having capacity of conducting strong currents. The strong currents are diverted to the metallic structure by a protection sleeve and a diversion member being in electrical contact with the protection sleeve and the metallic structure. By this arrangement, the strong currents are effectively led to run through the surge protection arrangement instead of through the coating of the casing and/or the connector body.
The metallic structure includes, in different embodiments of the invention, a metallic structure in the form of a mounting bracket, a support construction, a lid closing the casing, a trimming plate, and/or a grounding braid. These different embodiments of the present invention all efficiently protect the device from surges and have further different advantages relating to the mounting conditions for the device. These embodiments, for surge protection purposes, make use of parts already being present in the device, such as the lid or the trimming plate, or in the mounting situation, such as the mounting bracket and the support construction, which, of course, is very cost effective and requires no extra mounting space.
According to one embodiment of the present invention, the diversion member includes a metal strip, having a contact portion essentially corresponding in shape to the shape of an end portion of the protection sleeve. According to another embodiment of the invention, the shape of the end portion of the contact portion essentially corresponds to the shape of the external wall surface of the protection sleeve. These two embodiments offer very good electrical contact between the protection sleeve and the diversion member when they are pressed axially and radially against each other, respectively.
According to one embodiment of the present invention, the diversion member includes one or more screws. This is advantageous, since the screws can also be used for attaching the device to the mounting bracket or the support construction, or can be used for securing the lid to the casing.
Detailed exemplary embodiments and advantages of the surge protection arrangement according to the invention will now be described with reference to the appended drawings illustrating some preferred embodiments.